Werner chromium complexes and method for their preparation

ABSTRACT

A WERNER COMPLEX COMPOSITION HAS TRIVALENT CHROMIUM ATOMS COORDINATED WITH ACIDO GROUPS AND FLUORINE ATOMS. THE ACIDO GROUPS ARE FROM SATURATED ALIPHATIC DICARBOXYLIC ACIDS HAVING LESS THAN SIX CARBON ATOMS AND THAT MAY CONTAIN HYDROXYL GROUPS, BUT NOT MORE THAN THREE HYDROXY GROUPS. THE COMPLEXES ARE CHACTERIZED BY A SPECIFIC RANGE FOR THE RATIO OF BOTH THE CHROMIUM ATOMS TO ACIDO GROUPS AS WELL AS CHROMIUM ATOMS TO FLUORINE ATMS. THE COMPLEX COMPOSITION IS USEFUL IN PREPARING CHROMIUM PLATING PATHS THAT HAVE A BRIGHT PLATING RANGE THAT IS DESIRABLY EXTENDED OVER ABROAD RANGE FOR DECORATIVE CHROMIUM PLATE.

United States Patent Ofice 3,733,346 Patented May 15., 1973 US. Cl. 260438.5 C 13 Claims ABSTRACT OF THE DISCLOSURE A Werner complex composition has trivalent chromium atoms coordinated with acido groups and fluorine atoms. The acido groups are from saturated aliphatic dicarboxylic acids having less than six carbon atoms and that may contain hydroxyl groups, but not more than three hydroxy groups. The complexes are characterized by a specific range for the ratio of both the chromium atoms to acido groups as well as chromium atoms to fluorine atoms. The complex composition is useful in preparing chromium plating paths that have a bright plating range that is desirably extended over a broad range for decorative chromium plate.

BACKGROUND OF THE INVENTION Formerly it has been shown to form complex compounds of the Werner type with trivalent nuclear chromium atoms and acyclic or carbocyclic, carboxylic acido groups, using for the complexing action acids containing ten or more carbon atoms, i.e., typically long chain acids. The chromium atoms could also be further coordinated, with neutral or monovalent groups, but this was of secondary importance. Representative of such groups have been the aquo, chloro, fluoro, bromo, formato, acetato and nitrato groups. The hydrophobic characteristics of surfaces treated with such compositions have been shown, for example, in US Pats. 2,273,040 and 2,356,161.

It has been further shown, for example in US. Pat. 2,524,803, that in a special process, other carboxylic acids may be useful, but, because of the nature of the special process disclosed, any halogen present in the complex is chloride. Although the typically long chain acids such as stearic may be used in this special process, and the resulting complex exploited for its hydrophobic quality, shorter chain acids, including monocarboxylic and dicarboxylic acids, and further including unsaturated acids, are also employed. These complexes from the shorter chain acids are of interest for their bonding capabilities, es pecially to polymers, and thus find utility in sizing glass fiber rovings used as plastic and resin reinforcements.

It has also been heretofore taught that acids which are not of the long chain type, and that most especially contain amine groups, but can be simple monocarboxylic acids containing not just one or a few, but very many hydroxyl groups, may be complexed with nuclear trivalent chromium to form compositions of the Werner type. The metal may be further coordinated with neutral groups such as aquo or negative monovalent groups, chloro, bromo, formato, acetato and nitrato being taught in US. Pat. 2,544,668. This patent additionally discloses the desirable bonding between surfaces of diverse materials, particularly polymers, that can be obtained by such Werner complex compounds.

Turning to electrolytic operations, US. Pat. 3,006,823 teaches that oxalic acid may be complexed with trivalent chromium and the complex may be used to form an aqueous electrolytic plating bath for the plating of bright chromium plate. Such bath can be of interest for the capability of depositing an acceptably bright plate at current densities within the range from 10-200 ampers per square foot (a.s.f.).

SUMMARY OF THE INVENTION The composition of the Werner complex described herein has trivalent chromium atoms coordinated with fluorine atoms and with acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and that may contain hydroxyl groups, but not more than three, and preferably only one, hydroxyl group when present at all. The complex finds particular utility in the preparation of an aqueous electrolytic plating bath for the deposition of bright chromium plate. The complex provides a decorative plate with a desirable bright finish and has a desirably extended bright range for the chromium plate. The complex of the present invention exhibits desirable water solubility, plus excellent plating utility over an extended pH range without dissociation or solids precipitation.

Broadly, the invention is directed to a composition of a Werner complex of trivalent chromium atoms coordinated with the acido groups of saturated aliphatic dicarboxylic acid having less than six carbon atoms and 0 to 3 hydroxyl groups, where possible, with the acid providing such complex with a ratio of total chromium atoms to total acido groups within the range of 1:0.7 to 1:3, such complex being further characterized by containing coordinated fluorine atoms and having a ratio of total chromium atoms to total fluorine atoms within the range of 1:01 to 1:3.5.

The invention is further directed to the preparation of a composition of a Werner complex containing trivalent chromium atoms coordinated with fluorine atoms and with acido groups of such saturated aliphatic dicarboxylic acid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The complexes of this invention are completely miscible in all proportions in water and exhibit a rich deep greenish color in water solution. Solubility in organic solvents, for example aprotic organic solvents, will vary ac cording to the particular solvent used, but typically will exhibit greater than slight solubility in dimethylformamide and dimethylacetamide. Solutions exhibit extended storage stability and may be neutralized, or changed over to even an alkaline pH, without solids precipitation.

The complexes of this invention can be prepared by any of several methods. One method is the straightforward combination 'in aqueous medium of chromium metal, preferably in pulverulent form to enhance completion of the reaction, with the dicarboxylic acid plus fluorine-providing compound. When particulate metal is used, the reaction can be highly exothermic and thus cau tion needs to be taken in carrying out such reaction. Typically for enhanced reaction efficiency, as the reaction proceeds and the evolved heat starts to diminish, external heating is applied and is continued with the aqueous medium being heated at reflux to augment completion of the reaction.

The complexes may also be prepared by the blending together of the dicarboxylic acid and the fluorine-providing compound in an aqueous reaction medium to which there is charged chromic acid, suitably as a solution of chromic acid in water. The chromic acid can be supplied by any of the substances for forming chromic acid in water, e.g., chromium trioxide. The reaction resulting from this method is also exothermic and caution in the use of such method is also thus advisable. In either of these methods, the fluorine-providing substance may be first re placed during reaction by a suitable chlorine-supplying compound such as hydrochloric acid. Such initial reaction therefore provides a complex containing chlorine from which the fluorine-containing complex can be derived by adding to the complex, suitably the reaction medium, a fluorine-providing compound and extending the reaction with heating for a time sufficient to displace chlorine atoms in the complex with fluorine atoms.

Other methods can be used to prepare the complex; for example, into about weight parts of water there can be dissolved about 10.5 weight parts of chromium fluoride (CrF -9H O) and, for preparing a complex where the saturated aliphatic dicarboxylic acid is oxalic acid, typically there can then be added about 5.5 weight parts of oxalic acid. While this mixture is constantly agitated there is gradually added thereto about 3.5 weight parts of potassium hydroxide. During the addition of the potassium hydroxide the reaction is exothermic and, as agitation of the mixture is continued, external heating is suitably applied until the mixture is brought to reflux. The mixture can then be maintained at reflux, typically for several hours, and upon cooling an aqueous solution of the complex from the oxalic acid, with fluorine, is obtained.

The saturated aliphatic dicarboxylic acids have less than six carbon atoms and zero to three hydroxyl groups and preferably, for economy, have two to four carbon atoms with no hydroxyl group. Thus in addition to oxalic acid the acids of particular interest include malonic, with the mono-hydroxy, saturated aliphatic acids much as malic acid being also advantageous. The source of the fluorine atoms for the complex can be, as mentioned hereinbefore, a fluoride salt of chromium. Other suitable sources of fluorine atoms, especially where the chromium is not present as a fluoride salt, include hydrogen fluoride, sodium fluosilicate, and gaseous fluorine.

Regardless of the acid used and the source of fluorine, the complex should contain a molar ratio of total chromium atoms to total carboxyl constituent within the range of 120.7 to 1:3, and further contain a molar ratio of total chromium atoms to total fluorine atoms within the range of 1:01 to 1:3..5. Especially preferred ratios, which are based upon the utility of the complex in an aqueous plating bath for the deposition of decorative chromium plate, can depend upon the acid constituent of the complex. Thus, for example, in a complex Where oxalic acid supplies a substantial amount of the carboxyl constituents, the molar ratio of all of the chromium atoms to all of the acido groups, i.e., to carboxyl constituent, is within the range of 121.9 to 1:2.6 and the molar ratio for such a complex of all chromium atoms to the total of the fluorine atoms is preferably within the range of about 1:2.6 to 1:32.

For preparing a chromium plating bath for the deposition of bright chromium plate the complex is generally supplied to a plating medium in an amount providing about -150 grams of chromium per liter. The more highly concentrated baths are well suited for spot plating techniques while the baths containing the lesser concentrations of chromium are useful for immersing therein articles to be plated. Before deposition of chromium such baths are adjusted to a pH within the range from about 1.8 to 4.9 which can be readily handled by the addition of an alkali metal carbonate or hydroxide. The temperature of the bath during plating may range from about 20 C. up to not substantially above about 50 C. for enhanced plating performance.

The bath can also contain a salt of a strong acid preferably, for economy, an alkali metal salt. Such baths may further contain boric acid, or an equivalent to boric acid in aqueous solution, to augment the rate of deposition of the chromium. The alkali metal salts are usually present in an amount of about 50200 grams per liter of the bath and the boric acid in an amount between about 10- 70 grams per liter of the bath. During plating, the object to be plated is made the cathode, for example, immersed in the plating bath, or the cathode in a brush plating operation when the plating medium is contained in a brush, and an inert anode is used, such as a graphite anode. The surfaces that can be plated from such a bath, include metals such as steel, brass, copper, nickel and the like as well as plastic surfaces that are activated or prepared for an electroplating operation. The plating can be carried out in any vessel useful for chromium electroplating such as tanks lined with corrosion resistant materials including glass ceramic material, polyvinyl chloride and the like.

EXAMPLE An exemplary complex from oxalic acid, prepared as described hereinabove with chromium fluoride in water, and where the external heating is applied until the mixture is brought to reflux and maintained there for several hours, is adjusted with additional water to provide the chrome complex solution with 40 grams per liter (g./l.) of chromium. The resulting solution is a clear, deep greenish solution that exhibits excellent extended storage stability without solids precipitation or color change. The solution contains a molar ratio of total chromium to total oxalic acid of 1:2.25 and a molar ratio of all chromium atoms to the total of the fluorine atoms of 1:2.8 8. A portion of the chrome complex solution is blended with potassium hydroxide in sufficient amount to change the pH of the portion from acid, past neutral, over to an alkaline pH greater than 8. Upon visual inspection, such alkaline chrome complex solution is seen to be free from color change or visible solids precipitation.

To demonstrate the plating characteristics of such chromium complex solution, suflicient complex solution can be prepared as described above to contain 40 g./l of chromium, and to this can be blended 60 g./l. of H BO and 150 g./l. of potassium chloride, with agitation. The pH of the solution is adjusted to 3.0 and during blending and pH adjustment the volume of the solution is adjusted to 1 liter by the addition of deionized water.

For this demonstration the resulting solution can be placed in a modified Hull cell which is a trapezoidal box of non-conductive material at the opposite ends of which are positioned anode and cathode plates, as has been more particularly described in an article appearing in Plating volume 46, Number 3 (1959), Page 257. For this cell it is possible to readily determine the effective plating range of a composition under varying conditions. The current density at any point on a cathode is determined according to the formula A=C (27.7-48.7 log L) wherein A is the current density in amps per square foot (a.s.f.) at the selected point, C is the total current in amps applied to the cell, and L is the distance in inches of the selected point from the high current density of the plate. In the cell graphite anodes are used and the cathode is 3 x 2% brass panel that is nickel coated prior to use in the cell.

In this cell plating tests are carried out at a constant bath temperature of about F. and at a constant voltage of about 14 volts using 10 amperes current for a 3 minute cycle. From such tests the bright range of decorative chromium plating can be seen to be desirably extended from below about 10 a.s.f. to greatly more than 350 a.s.f., which is highly desirable for decorative chromium plating. A panel deposit of a rich and deep appearance can be observed, and of a slightly darker cast than that observed with commercially available decorative chromium deposits from hexavalent chromium plating baths.

What is claimed is:

1. A composition of a Werner complex of trivalent chromium atoms coordinated with acido groups of saturated aliphatic dicarboxylic acid selected from the group consisting of oxalic acid, malonic acid, and mixtures thereof, said acid providing said complex with a ratio of total chromium atoms to total acido groups within the range of 1:07 to 1:3, said complex being further characterized by containing coordinated fluorine atoms and having a ratio of total chromium atoms to total fluorine atoms within the range of 1:01 to 1:3.5.

2. A composition as set forth in claim 1 wherein said saturated aliphatic dicarboxylic acid of said Werner complex is oxalic acid.

3. The method for the production of a composition of a Werner complex having trivalent chromium atoms coordinated with fluorine atoms and with acido groups of saturated aliphatic dicarboxylic acid selected from the group consisting of oxalic acid, malonic acid, and mixtures thereof, which method comprises:

(1) establishing a liquid, aqueous reaction medium containing chromium metal, withsufiicient of said carboxylic acid to provide said medium with a molar ratio of total chromium atoms to total acido groups within the range of 1:0.7 to 1:3, and with suflicient fluorine-providing compound to supply said reaction medium with a molar ratio of total chromium atoms to total fluorine atoms within the range of 1:01 to 123.5; and

(2) permitting reaction of the substituents in said medium.

4. The process of claim 3 wherein said fluorine compound is selected from the group consisting of hydrogen fluoride, sodium fluosilicate, fluorine gas, and mixtures thereof.

5. The process of claim 3 wherein said saturated aliphatic dicarboxylic acidis selected from the group consisting of oxalic acid, malonic aid, and mixtures thereof.

6. The process of claim 3 wherein water supplies all of the liquid of said reaction medium, such medium is heated to boiling during reaction, and said chromium metal is in pulverulent form.

7. The process for preparing a composition of a Werner complex containing trivalent chromium atoms coordinated with fluorine atoms and with acido groups of saturated aliphatic dicarboxylic acid selected from the group consisting of oxalic acid, malonic acid, and mixtures thereof, which process comprises:

(1) bringing together in water supplying liquid for a reaction medium, chromic acid with suflicient of said dicarboxylic acid to provide said medium with a molar ratio of total chromium atoms to total acido groups within the range of 1:0.7 to1:3, and with fluorine-providing compound suflicient to supply said medium with a molar ratio of total chromium atoms to total fluorine atoms within the range of 1:0.1 to 113.5; and

" (2) permitting reaction of the substituents in said medium.

8. The process of claim 7 wherein said fluorine-providing compound is selected from the group consisting of hydrogen fluoride, sodium fluosilicate, fluorine gas, and mixtures thereof.

9. The process of claim 7 wherein said saturated aliphatic dicarboxylic acid is selected from the group consisting of oxalic acid, malonic acid, and mixtures thereof.

10. The process for producing a composition of a Werner complex having trivalent chromium atoms coordinated with fluorine atoms and with acido groups of saturated aliphatic dicarboxylic acids selected from the group consisting of oxalic acid, malonic acid and mixtures thereof, which method comprises:

(l) establishing a liquid, aqueous reaction medium containing chromium-providing material selected from the group consisting of chromium metal, chromic acid, and mixtures thereof, in mixture with said dicarboxylic acid in amount sufficient to provide said medium with a molar ratio of total chromium atoms to total acido groups within the range of 1:0.7 to 1:3, and further with chlorine-providing compound sufficient to supply said medium with a molar ratio of total chromium atoms to total chlorine atoms within the range of 1:0.1 to 1:35;

(2) permitting reaction of the substituents in said medium thereby preparing a composition of a Werner complex having trivalent chromium atoms coordinated with chlorine atoms and acido groups;

(3) furnishing said medium containing said complex with sufficient fluorine-providing compound to supply said medium with a molar ratio of total chromium atoms to total fluorine atoms within the range of 1:0.1 to 1:35; and

(4) heating the resulting medium at elevated temperature and for a time suflicient to displace chlorine atoms in said complex with fluorine atoms.

11. The process of claim 10 wherein said medium containing said complex is furnished with suflicient fluorineproviding compound to supply therein a stoichiometric excess of fluorine atoms, basis moles of chlorine atoms in said medium.

12. The process of claim 10 wherein said chlorine-providing compound is selected from the group consisting of hydrochloric acid, chlorine gas, and mixtures thereof.

13. A composition as set forth in claim 1 wherein said saturated aliphatic dicarboxylic acid of said Werner complex is malonic acid.

References Cited UNITED STATES PATENTS 2,524,803 10/ 1950 Iler 260438.5 C 2,273,040 2/ 1942 Iler 260-438.5 C 2,544,666 3/1951 Goebel et al. 260438.5 C 2,544,667 3/1951 Goebel et al. 260438.5 C 2,544,668 3/ 1951 Goebel et al. 260438.5 C 2,825,659 3/1958 Dalton et al. 260438.5 C 3,137,717 6/1964 Peters 260438.5 R 3,136,796 6/ 1964 Trebilcock 260438.5 R 3,185,717 5/1965 Trebilcock 260438.5 R

OTHER REFERENCES Sidgwick, The Chemical Elements and Their Compounds, Oxford Univ. Press, London, vol. H p. 1023 Chemical Abstracts, vol. 60, 12247d (1964). Chemical Abstracts, vol. 44, 3393d (1950). Chemical Abstracts, vol. 47, 12087f (1953). Chemical Abstracts, vol. 41, 2925b (1947).

Chemical Abstracts, vol. 49, l0783g (1955).

HELEN M. S. SNEED, Primary Examiner US. Cl. X.R. 117-l07.2

i I UNITED STATES PATENT OFFICE 69 CERTIFICATE OF CORRECTION Patent No. 3.133.346 Dated May 15, 1973 Inirentofls) John Edwin Bride It is certified that error appears in the above-identified patent and that said Letters Patept are hereby corrected as shown below:

Column 5 line 19, "1:01" should read --1 =o.1--. Column 5,' line 29, '"aid" should read -acid-.

Signed; ahd sealed this 5th day of March 19m.

(SEAL) Attest:

EDWARD M.FLET-CHER,JR. Attesting Officer -c. MARSHALL DANN Commissioner of Patents 

